A moving object recognizer has been developed to recognize a change in the velocity and motion of an object such as a pedestrian, a vehicle ahead and find a dangerous situation as a pedestrian's sudden jumping-in, another vehicle's cutting-in, to be able to warn a driver thereof for prevention of such a danger.
For example, there is a technique for moving object recognition to find a change in the distance to a moving object ahead according to a change in the size of the moving object between two-dimensional image frames and the focal length of a camera. However, this technique cannot accurately measure the distance to the moving object or accurately detect a change in the motion of the object.
In view of the above, Japanese Patent Application Publication No. 2000-266539, for instance, discloses an inter-vehicular distance measuring unit for calculating a disparity from a stereo image obtained with a stereo camera to generate a disparity image or a range image. The disparity image refers to an image whose pixel value is a disparity value.
This measuring unit is configured to detect a vehicle ahead from the disparity image, find a moving vector of the edge of the vehicle, and calculate an inter-vehicular distance and a change in the distance according to the magnitude and direction of the moving vector.
This measuring unit recognizes a moving object from the disparity image alone and obtains the disparity image by image matching in unit of block or window. Because of this, it has a drawback that the spatial resolution of the disparity image is low. For instance, it cannot accurately detect the distance to a vehicle ahead having a non-planar rear part.